Diesel fuel is a mixture of a variety of hydrocarbons. Most of the hydrocarbons are aliphatic, but aromatics may be present at up to twenty to twenty five weight percent of the fuel. The mixture can also include kerosine or gas oil. Diesel fuel is commonly used in motor vehicles, and has a tendency to foam profusely when it is poured into the fuel tank of a motor vehicle. It is therefore desirable to reduce such foaming, which can be accomplished by the addition of a defoamer.
Oil companies treat diesel fuel with organic additives, such as detergents, cetane improvers, viscosity breakers and occasionally perfumes, frequently as a preblended mixture of additives collectively referred to as a "DAP". Each oil company has its own preferred DAP which it typically uses only for mixing with its own fuel. All of these organic additives must be compatible with the defoamer.
Diesel fuels delivered to filling stations also may contain some amount of dispersed or dissolved water which can adversely affect the performance characteristics of previously known defoamers. The water causes a decay in defoaming characteristics and in some extreme cases, may cause the defoamer to enhance foaming, rather than suppress it. Such wet defoamers also can result in increased sludge deposition in the fuel tank.
Certain silicones are known to defoam diesel fuel. However, the introduction of silicon into engine systems can have adverse effects so there exists a need to provide low silicon content defoaming systems for diesel fuel applications.
U.S. Pat. No. 4,690,688 issued to Adams et al. discloses a polysiloxane for use as a defoamer, wherein the polysiloxane is a copolymer with polyether side chains that provide at least 25 weight percent of the copolymer. However, these polysiloxane copolymers do not work well in wet diesel fuel because the ethers, as a hydrophilic material, will tend to stabilize the foaming of wet fuel. Additionally, to function properly these polysiloxanes must be present at levels in diesel fuel above those desirable in engine systems.
DE 4032006 describes a process for defoaming and/or degassing organic systems, including diesel oil, by adding a foam suppressant containing an organopolysiloxane with unsaturated sidechains. A disadvantage of this foam suppressant is that it contains high levels of silicon, which can be harmful to engines. In addition, it can be incompatible with some DAPs and does not age well.
U.S. Pat. No. 5,542,960 describes a class of organosilicone terpolymers which may be used to abate the foaming of diesel fuel. The terpolymers are prepared by grafting phenol derivative substituents and polyether substituents onto a polymethylsiloxane so that the final siloxane polymer includes dimethyldisiloxy, methylphenolicdisiloxy and methylpolyetherdisiloxy units thereon.
EP 741182 describes silicone diesel defoamers which include, on the polyorganosiloxane backbone, a mixture of methyl groups, unsaturated polyhydric groups, polyether groups and phenol groups.
WO 97/38067 describes a class of polydiorganosilioxane polymers useful as diesel fuel defoaming agents which have a certain content of saturated organic groups which include at least two hydroxyl groups or derivatives thereof.
Recent diesel fuel specifications have resulted in redesigned additive packages which have increased compatibility problems with silicone defoamers, thereby creating a need for further improvements in silicone defoaming efficiency.